Inhomogeneous magnetoresistance devices

ABSTRACT

A solid state element having layer form inhomogeneities in impurity concentration is positioned within a magnetic field and experiences changes in resistance when subjected to energy in the form of a standing sound wave, a travelling sound wave, a change in direction of a magnetic field, or light in a pattern of alternating intensity.

0 United States Patent 1 3,569,895

[72] Inventor Hiroyuki Fujisada [51] lnt.Cl H0lc 7/16 Tokyo,Japan [50]Field ol'Search 338/13, 14, [21] App]. No. 833,489 15, 17, 32, 32 (H)[22] Filed June 16, 1969 4s 1 Patented Mar. 9, 1971 [561 References CM[73] Assignee Agency of Industrial Science & Technology, UNITED STATESPATENTS Ministry of Internati nal Tra e & In u ry 2,894,234 7/1959 Weisset a1 338/32 ymJ p 3,143,448 8/1964 Mette m1 338/32X [32] Priority Aug.15,1966 3,286,161 11/1966 Jones et a1. 338/32X EI/ 270 27 3,382,4485/1968 Oberg et a1. 338/32X [31] 53 and4l 53 1 Continuation-impart ofapplication Ser. No. i p g 1 Barney 661,757, Aug. 4, 1967, nowabandoned.

Att0rneyl(urt Kelman ABSTRACT: A solid state element hairing in- [54]gggggg MAGNETORESISTANCE homogeneities in impurity concentration ispositioned within a mu 12D Fi magnetic field and experiences changes inresistance when rawmg subjected to energy in the form of a standingsound wave, a [52] U.S.Cl 338/14, travelling sound wave, a change indirection of a ma netic g 338/ 17, 338/32 field, or light in a attern ofalternating intensit Patented March 9,1971

4 Sheets-Sheet 1 INVENTOR i-uaov'um UJ|5A A AGENT I Patented I March 9,1971 3,569,895

4 Shets-Sheet z I NVENTOR mowm :FUJIMDA BY W Patented March 3,569,895

I I 4 Sheets-Sheet s I I mung v w INVENTOR AGENF' Patented March 9,19713,569,895

4 Sheets-Sheet 1L INVENTOR INIIOMGGENEOUS MAGNETORESISTANCE DEVICESREFERENCE TO RELATED APPLICATION This is a continuation-in-part of myapplication Ser. No. 661,757, filed Aug. 4, 1967, now abandoned.

This invention relates to a magnetoresistance device utilizing the sharpangle dependence of the magnetoresistance effeet in a solid stateelement having layer form inhomogeneities in carrier concentrations. Itfurther relates to a magnetoresistance device utilizing the dependenceof the magnetoresistance effect on the degree of inhomogeneities incarrier concentration.

In conventional devices utilizing the magnetoresistance effect, thedependence of electric resistance on the strength of the magnetic fieldis utilized. However, conventional devices are defective in thatsensitivity is low. Furthermore, devices such as transistors, vacuumtubes, and the like are likewise dethe input from the output isimpossible and, very often, conventional devices are unusable at highfrequencies.

The object of this invention is to provide inhomogeneousmagnetoresistance devices for use in amplification, oscillation,waveform conversion, frequency conversion or signal conversion which areof high sensitivity and fully utilizable even in the high frequencyregion.

The novel features that are considered characteristic of this inventionare set forth with particularity in the appended claims.'The inventionitself, however, both as to its organization and method of operation, aswell as additional objects and advantages thereof, will best beunderstood from the following description when read in connection withthe accompanying drawing wherein:

FIG. I shows an example of a solid state element having layer forminhomogeneities;

FIG. 2 and FIG. 3 each shows a plot of a form in which the impurityconcentration changes in the X direction of the structure of FIG. I;

FIG. 4 shows a curve of the angular dependence of the electricresistance of the solid state element illustrated in FIG. 1 for variousangles of magnetic field;

FIG. 5 illustrates structure of a device utilizing the sharp angulardependence of the electric resistance of a solid state element havinglayer form inhomogeneities;

FIGS. 6 to 8 illustrate three kinds of relationships between the inputsignal and output signal of the device illustrated in FIG. 5;

FIG. 9 shows the change in electric resistance for various degrees ofinhomogeneities;

FIGS. 10 and 11 each shows structure in accordance with the principlesof this invention for converting a sound wave into an electricsignal;and

FIG. 12 shows structure in accordance with the principles of thisinvention for converting light into an electric signal.

The term angle" used herein refers to the angle between the direction ofthe magnetic field and the current direction, i.e. longitudinaldirection, of the solid state element. Also, the term "layer forminhomogeneities" refers to the inhomogeneities in structure wherein thinplatelike materials which differ in impurity concentration arealternately positioned adjacent to each other (see FIG. 2). When theplatelike materials become infinitely thin, the impurity concentrationchanges continuously in a certain specific direction (see FIG. 3).

As is well known, the magnetoresistance effect (meaning the effect ofthe change in electric resistance under a magnetic field) of asolid-state element with high electron mobility such small. Accordingly,the cases of utilizing the effect of inhomogeneities are divided intotwo types, one utilizing the sharp angle dependence under a fixed degreeof layer form inhomogeneities in impurity concentration and the otherone utilizing the change in resistance caused by changing the degree ofinhomogeneities in electron concentration.

FIG. 1 shows an example of the solid state element having layer forminhomogeneities in the longitudinal direction (x direction). The solidand dashed lines in FIG. 1 show the maximum and minimum values ofelectron concentration, respectively. FIG. 2 and FIG. 3 each shows theform in which the impurity concentration changes in the x direction. Theforms shown in FIGS. 2 and 3 are typical examples. However, the impurityconcentration need not always change in such forms.

FIG. 4 shows the state of change in electric resistance in the case.where a constant magnetic field is applied to the solid state elementillustrated in FIG. 1 while the angle of said magnetic field to thelongitudinal direction of said solid state element is changed. In FIG.4, the solid line curve shows the characteristics in the case where thesolid state element has layer form inhomogeneities; and, the dashed linecurve shows the characteristics in the case where said element is devoidof said inhomogeneities. FIG. 4 illustrates clearly the effect of layerform inhomogeneities. It is to be noted that in the vicinity of g theangular dependence of electric resistance becomes strikingly great.Accordingly, if a constant magnetic field which is applied at an anglecorresponding to the points A, B or C shown in FIG. 4, was changedslightly be some means, a great change in electric resistance would beobtained.

FIG. 5 shows an embodiment changing the angle of a magnetic fieldelectrically. Solid state element 1 having layer form inhomogeneities isin a constant bias magnetic field applied by a permanent magnet orelectromagnet 2. Coil 4 is adapted to excite a magnetic field in thelongitudinal direction of the solid state element 1. Now, if an inputsignal voltage Vin" is applied to the coil 4, the direction of resultantmagnetic field slightly changes because the magnetic field generated bythe coil 4 differs in direction from the constant bias magnetic field.As already stated, the electric resistance between the electrodes 3, 3'of solid state element 1 tends to change easily by the change in thedirection of a magnetic field. Therefore, this electric resistancechanges greatly according to the input signal. When a voltage source 5is connected through a load resistance 6 between the electrodes 3, 3',an output signal voltage Vout is produced across said load resistance.

The above embodiment can be applied to various uses by selecting anappropriate angle go of the bias magnetic field relative to thelongitudinal direction of the solid state element 1.

FIGS. 6 to 8 each shows the relationship between the input signal andthe output signal in the case where the angle L0 is set to correspond tothe respective points A, B and C in FIG. 4. In FIG. 6 a bias magneticfield is applied in the direction in which the angular dependence isgreatto produce a great change in resistance with a small amount ofinput signal voltage Vin". This embodiment finds application in anamplifier.

In FIG. 7 a bias magnetic field is applied in the direction in which theresistance is greatest. This embodiment finds application in a frequencymultiplier. In FIG. 8, by applying a bias magnetic field to the point Cwhere the angular dependence is small it is possible to convert theinput voltage of rectangular wave form into an output voltage of sharppulse form. In addition to the embodiments shown, it is also possible,by utilizing the angle dependence of the layer form inhomogeneousmagnetoresistance effect, to effect conversion of various otherwaveforms and frequencies. Further, the embodiments illustrated can beutilized as highly sensitive variable resistance elements in variouselectric circuits.

The structure of FIG. 5, when positioned to utilize the sharp angledependence exhibits high amplification characteristic. Because of thishigh sensitivity, there are many advantages. The gains of amplifiers andthe conversion efficiencies of waveform converters or frequencyconverters can be made very high. Also, when an input signal is fed tothe invention as illustrated in FIG. 5, complete isolation is obtainedbetween the input signal and the output signal.

FIG. 9 illustrates the change in electric resistance in the case wherethe degree of inhomogeneities is changed under constant magnetic field BIn this instance, the inhomogeneities need not always be in layer form.In the plot of FIG. 9, n, represents the mean value of the carrierconcentrations: An, represents the deviation from said means value,

represent the means value of (An)? Accordingly, the abscissa is astandard deviation of the carrier concentration. B B and 13, eachrepresents a certain specific value of bias magnetic field 3,. SinceB,,, B,, B,, the stronger the bias magnetic field, the greater theeffect of inhomogeneities. If inhomogeneities are formed in the carrierconcentration by an input signal, a change in resistance of the solidstate element will result and the output can be obtained as an electricsignal.

FIGS. 10 and 11 each illustrates an embodiment where the degree of layerform inhomogeneities is changed by a sound wave to convert a sound waveinto an electric signal. Referring specifically to FIG. 10. A sound waveis introduced through a sound wave conducting medium 9 into an end of ahomogeneous solid state element 7 having an electron of high mobilitysuch as lnSb, the other end of said solid state element being connectedto a mismatching load 8. The sound wave then propagates in standing waveform in the solid state element, and, due to the interaction between thesound wave and the electron, the electron concentration changes not onlyas time elapses but even spacially with the same periodicity as thesound wave. In this case, because the sound wave is in standing waveform, the electron concentration is also in standing wave form. Thedegree of inhomogeneities changes at a frequency that is double (2times) that of the sound wave, where An is a deviation from the meanvalue n, of electron concentration. Accordingly, if a constant biasmagnetic field is applied to the solid state element 7 by a permanentmagnet or electromagnet 2, the electric resistance between theelectrodes 3, 3 changes at a frequency double (2 times) that of thesound wave. If an electric current is constantly applied from a voltagesource 5 through a load resistance 6 to the electrodes 3, 3', thevoltage at both ends of said load resistance changes at a frequency thatis double (2 times) that of the sound wave, and this change in voltagecan be detected by a detector means 10.

FIG. 11 illustrates an embodiment using a matching load 8 in place ofthe mismatching load 8 in FIG. 10. In this case, the sound wave is intravelling wave form in the solid state element, and, accordingly, theelectron concentration is also in travelling wave form. The degree ofinhomogeneities in electron concentration does not change as timeelapses, but the electric resistance alone between the electrodes 3, 3'changes according to the input sound wave. The change in resistancebetween the electrodes 3, 3 can be detected by a detector means 14through the bridge network in which the solid state element 7 is set asone of the arms thereof.

The solid and dashed lines on the respective solid state elements 7 inFIGS. 10 and 11 show the maximum and minimum values of spacedistribution of electron concentration at a specific instant of time.

FIG. 12 illustrates an embodiment changing the degree of inhomogeneitiesin electron concentration by light to convert light into an electricsignal. Solid state element 18 is disposed in inclined form so that botha magnetic field excited by a permanent magnet or electromagnet 2 andlight may be applied simultaneouslyto said solid state element. A lightshield plate 19 with interstices is mounted onthe solid state element 18so that light may be applied only to a portion of said solid stateelement. When light is applied through said shield plate to the solidstate element 18, the electron concentration increase only in thoseportions of said element that are exposed to the light. Accordingly, thedegree of inhomogeneities in electron concentration and consequently theresistance between the electrodes 3, 3 located at both ends of the solidstate element 18 disposed in the magnetic field increases. This increasein resistance due to the application of light can be detected by adetector means 14 of the bridge network in which the solid state element18 is set as an arm thereof.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is, therefore, to beunderstood that the invention may be practiced otherwise than asspecifically described herein.

I claim:

1. A magnetoresistance device comprising a solid state element havinglayer form inhomogeneities in impurity concentration, means to apply aconstant bias magnetic field to said solid state element, a coil togenerate a second magnetic field which differs in direction from saidconstant bias magnetic field to change the direction of resultantmagnetic field, the resistance of said solid state element beingdetermined by the direction of said resultant magnetic field.

2. The structure of claim 1 wherein said means to apply a constant biasmagnetic field to said solid state element comprises a magnet.

3. The structure of claim 1 wherein said solid state element is orientedto said constant bias magnetic field to exhibit a maximum angulardependence of resistance.

4. The structure of claim 3 including means sensitive to changes in theresistance of said solid state element.

5. The structure of claim 4 wherein said means sensitive to changes inthe resistance of said solid state element comprises a source ofpotential coupled to said solid state element, and a load impedancecoupled to exhibit changes of potential across said solid state element.

6. The structure of claim 1 wherein said solid state element is disposedwithin and oriented to said constant bias magnetic field to exhibit amaximum resistance.

7. A magnetoresistance device for converting a sound wave into anelectric signal comprising a magnet for supplying a constant magneticfield, a solid state element having layer form inhomogeneities inimpurity concentration and positioned within said magnetic field, meansfor introducing a sound wave to one of said opposing ends of said solidstate element, load means for said sound wave coupled to the other ofsaid opposing ends of said solid state element wherein the resistance ofsaid solid state element is changed by the introduction of a sound waveto the opposing end, and means coupled to detect changes in theresistance of said solid state element.

8. The structure of claim 7 wherein said load means comprises amismatching load for said sound wave to generate the standing sound wavein said solid state element whereby the resistance of said solid stateelement changes at a frequency double that of the sound wave and saidmeans coupled to detect changes in the resistance of said solid stateelement generates a signal having a frequency double that of the soundwave.

9. The structure of claim 7 wherein said load means comprises a matchingload for said sound wave to generate the travelling sound wave in saidsolid state element.

10. A magnetoresistance device for converting light into an electricsignal comprising a magnet for supplying a constant magnetic field, asolid state element having layer form inhomogeneities in impurityconcentration and positioned within said magnetic field, element, alight shield plate interposed between said solid state element and saidmeans and having interstices adapted to pass light only to a portion ofsaid solid state element, and means for detecting changes in resistanceof said solid state element due to the inhomogeneities in electronconcentration of said solid state element caused by the partialapplication of light to said solid state element.

1. A magnetoresistance device comprising a solid state element havinglayer form inhomogeneities in impurity concentration, means to apply aconstant bias magnetic field to said solid state element, a coil togenerate a second magnetic field which differs in direction from saidconstant bias magnetic field to change the direction of resultantmagnetic field, the resistance of said solid state element beingdetermined by the direction of said resultant magnetic field.
 2. Thestructure of claim 1 wherein said means to apply a constant biasmagnetic field to said solid state element comprises a magnet.
 3. Thestructure of claim 1 wherein said solid state element is oriented tosaid constant bias magnetic field to exhibit a maximum angulardependence of resistance.
 4. The structure of claim 3 including meanssensitive to changes in the resistance of said solid state element. 5.The structure of claim 4 wherein said means sensitive to changes in theresistance of said solid state element comprises a source of potentialcoupled to said solid state element, and a load impedance coupled toexhibit changes of potential across said solid state element.
 6. Thestructure of claim 1 wherein said solid state element is disposed withinand oriented to said constant bias magnetic field to exhibit a maximumresistance.
 7. A magnetoresistance device for converting a sound waveinto an electric signal comprising a magnet for supplying a constantmagneTic field, a solid state element having layer form inhomogeneitiesin impurity concentration and positioned within said magnetic field,means for introducing a sound wave to one of said opposing ends of saidsolid state element, load means for said sound wave coupled to the otherof said opposing ends of said solid state element wherein the resistanceof said solid state element is changed by the introduction of a soundwave to the opposing end, and means coupled to detect changes in theresistance of said solid state element.
 8. The structure of claim 7wherein said load means comprises a mismatching load for said sound waveto generate the standing sound wave in said solid state element wherebythe resistance of said solid state element changes at a frequency doublethat of the sound wave and said means coupled to detect changes in theresistance of said solid state element generates a signal having afrequency double that of the sound wave.
 9. The structure of claim 7wherein said load means comprises a matching load for said sound wave togenerate the travelling sound wave in said solid state element.
 10. Amagnetoresistance device for converting light into an electric signalcomprising a magnet for supplying a constant magnetic field, a solidstate element having layer form inhomogeneities in impurityconcentration and positioned within said magnetic field, element, alight shield plate interposed between said solid state element and saidmeans and having interstices adapted to pass light only to a portion ofsaid solid state element, and means for detecting changes in resistanceof said solid state element due to the inhomogeneities in electronconcentration of said solid state element caused by the partialapplication of light to said solid state element.